Wednesday, April 09, 2008

More on Telstar replacement centerboard and a bit of carbon wing mast planning

The ply/ss/foam centerboard tended to twist, that's why I decided to glass and bag one side at a time and " strap" the board against the table with vacuum while curing. This worked OK. I unwrapped today and it is now less twisted. It is, however, remarkable how stiff carbon is. I would expect the board to be stiffer with 200g carbon than it seems with 450g glass.

This is how the new board looks like in the correct orientation. The original had the curved part out on the right in this picture extending down to less than a foot from the bottom, leaving a lot of ineffective wetted surface. That's why, long before I decided to build a Farrier design, I started to plan a new board when I would find the time for it. I didn't, but finally had to..... Guess I need a new rudder as well quite soon.

Detail of the not-as-sophisticated-as-the-Farrier-boards Telstar replacement board. In stead of unidirectional carbon an ss reinforcement is rebated down each side, bolted and welded together. Guess it won't break in a breeze again. The several layers of ply and ss is wrapped in one layer of 450g 45/45 glass.

Eivind decided on the profile, and made the board, finishing and glassing left for me to do. I think it is a NACA 0012 profile. This is what it looks like anyway. The original board was a big rectangular underwater break.

I also borrowed Eivind's mast moulds. This mast was originally designed for the Mirage formula 28 trimaran and they are thus 7,5 m long, each one making one fourth of the mast. The mast is then 15m (49,2 ft), symmetrical around the mid point. It is (if you haven't already noticed on the above link) quite a bit bigger in the middle section and it does not carry spreaders or diamonds. If I decide to build from these moulds (the alternative is to buy a Marström mast) I guess I will place the fatter part at the spreader position, not at the center of the mast. And I will have to get someone do some calculations for me. I plan to make the mast foot an integrated part of the carbon construction. It is however tempting to go with the Martröm, details of such a mast made for a bigger F-boat here.

This is the middle section end of the moulds, measuring approximately 23 cm x 52 cm (9" x 20 1/2")

This is the top and bottom, approximately 10 cm x 29 cm (4 x 11 1/2")

I will be going on a short vacation, hopefully I will be able to finish the board laminations on Sunday evening and get on with the F-22 again.


Silas said...

Hi Tor,

I'll admit it, I'm biased (I want to know what the Marstrom mast costs all up), but my vote goes for the Marstrom spar. If you keep the mast height anywhere near the 35ft F-22R spec, you are cutting the mast down by at least 10ft. While extra strength is nice, this is going to leave you with an overly large mast section for the boat and thus extra weight. If the goal is performance, having a bunch of extra weight aloft is going to hurt more than anywhere else on the boat. Or are you thinking of doing a lighter laminate schedule for your boat to keep weight down?

MartinF said...

That Mirage looks very slim and fast. I cannot quite figure the measurements. Is the mast section 10 x 29 cm at the ends and 23 x 52 cm at the middle part? If so that is quite a stick and to big for you, and even for me. I plan for a 10 x 20-23 cm section, tapering at the top.

What is the molds made from, GRP or wood?

A Marström is very nice and very expensive.

Best luck
Lydius F82